Resistance of 'Tulare' Walnut (Juglans regia cv. Tulare) to aflatoxigenesis

The ability of tree nuts to inhibit production of aflatoxins by Aspergillus flavus was investigated in vitro. Walnuts were much more resistant to aflatoxin formation than almonds or pistachios. The walnut cultivar 'Tulare' showed complete suppression of toxin production. Kernel without seed coat had no activity and the inhibitory factor(s) were shown to be specifically located in seed coat tissue. When seed coat was added back to 'Tulare' kernel media, aflatoxin was decreased to the detection limit or below. Aflatoxin production declined rapidly with seed coat maturity and was independent of growing location and rootstock. Breeding programs could increase resistance, enhancing marketability and safety of walnuts for human consumption.